Well when I here "his spawn is completely random" and then a billion people saying "I found him in X box in WP/Opportunity" that makes me think certain things may cause him to spawn in a specific place.

With this Achievement being able to be unlocked now by people finding out how, I would like to think someone can come up with a spot to best look for JJ.

It's a domino effect... the guidebook says to go to that spot, so someone goes there and finds him at some point. After someone asks, person A says he found him there. People who know how to search see the post and try it out for their self. After X period they find him, which leads to several people claiming that he spawns there. Realistically, you have the same odds of finding him at any of those places (perhaps all of Pandora), so pick a place and farm.